The Marcellus Shale natural gas industry has a huge thirst for water - to hydraulically fracture a single gas well requires upward of a thousand tanker-trucks of water.
And so during the summer, when some streams here in gas-rich northern Pennsylvania naturally turn into trickles, the Susquehanna River Basin Commission pays close attention to ensure that drilling interests don't suck the state's creeks dry.
The SRBC, an interstate agency responsible for managing the Susquehanna watershed, this summer has suspended withdrawals from as many as 40 permitted locations because of seasonal low flows. Most of the suspended locations affect gas drillers.
But the shale-gas industry, now moving rapidly from an exploratory to a production phase, has hardly missed a beat. Fracking continues, largely unabated.
The commission allows drillers to withdraw up to 98 million gallons per day at 142 locations, though in reality, the industry uses far less than what it is allowed, the SRBC says. The permitted amounts are based on elaborate computations tied to historical stream flows. When stream levels fall below a certain level, withdrawals must stop.
Anticipating the seasonal fluctuations, natural gas operators have built vast networks of impoundments - plastic-lined ponds - to store water from the rainy seasons.